I asked a show person (unfortunately not one who has white dogs) and she said that there is a mixture that they use, just isn't sure what it is.
BUT apparently it can be treated homeopathically because staining is not something a healthy dog has. So maybe try to find a homeopathic vet in the area and make an appointment.
(And by saying the word "healthy" I don't in anyway mean to say that Riggs isn't healthy in the allopathic sense of the word. Rather in homeopathy health is looked at as a whole and so even a tiny thing that is off, like say weepy eyes or a hot spot, means that the dog isn't absolutely healthy, ie: the dog's body isn't running full force healthy . . . oh man that barely made any sense, I would have to go into a full on explanation of homeopathy and other holistic medicines to explain myself fully. It's too early in the morning for that.)
"All changes, even the most longed for, have their melancholy; for what we leave behind us is a part of ourselves; we must die to one life before we can enter another." -Anatole France